2.1 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition System Programs (p73) System programs provide a convenient environment for program development and execution. The can be divided into: File manipulation Status information File modification Programming language support Program loading and execution Communications Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls

2.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition System Programs Provide a convenient environment for program development and execution Some of them are simply user interfaces to system calls; others are considerably more complex File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories Status information Some ask the system for info - date, time, amount of available memory, disk space, number of users Others provide detailed performance, logging, and debugging information Typically, these programs format and print the output to the terminal or other output devices Some systems implement a registry - used to store and retrieve configuration information

2.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition System Programs (cont’d) File modification Text editors to create and modify files Special commands to search contents of files or perform transformations of the text Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another

2.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Operating System Design and Implementation(p74) Design and Implementation of OS not “solvable”, but some approaches have proven successful Internal structure of different Operating Systems can vary widely Start by defining goals and specifications Affected by choice of hardware, type of system( 일괄처리, 시분할, 단일 / 다중사용자, 분산, 실시간 ) User goals and System goals User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

2.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Operating System Design and Implementation (Cont) Important principle to separate Policy: What will be done? Mechanism: How to do it? Mechanisms determine how to do something, policies decide what will be done The separation of policy from mechanism is a very important principle, it allows maximum flexibility if policy decisions are to be changed later

2.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Simple Structure MS-DOS – written to provide the most functionality in the least space Not divided into modules Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated

2.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition MS-DOS Layer Structure

2.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition UNIX UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts Systems programs The kernel  Consists of everything below the system-call interface and above the physical hardware  Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level

2.9 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Traditional UNIX System Structure

2.10 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

2.11 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Layered Operating System

2.12 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Microkernel System Structure Moves as much from the kernel into “user” space Communication takes place between user modules using message passing Benefits: Easier to extend a microkernel Easier to port the operating system to new architectures More reliable (less code is running in kernel mode) More secure Detriments: Performance overhead of user space to kernel space communication

2.13 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Mac OS X Structure

2.14 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Modules Most modern operating systems implement kernel modules Uses object-oriented approach Each core component is separate Each talks to the others over known interfaces Each is loadable as needed within the kernel Overall, similar to layers but with more flexible

2.15 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Solaris Modular Approach

2.16 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Virtual Machines A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware A virtual machine provides an interface identical to the underlying bare hardware The operating system host creates the illusion that a process has its own processor and (virtual memory) Each guest provided with a (virtual) copy of underlying computer

2.17 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Virtual Machines History and Benefits First appeared commercially in IBM mainframes in 1972 Fundamentally, multiple execution environments (different operating systems) can share the same hardware Protect from each other Some sharing of file can be permitted, controlled Commutate with each other, other physical systems via networking Useful for development, testing Consolidation of many low-resource use systems onto fewer busier systems “Open Virtual Machine Format”, standard format of virtual machines, allows a VM to run within many different virtual machine (host) platforms

2.18 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Virtual Machines (Cont) (a) Nonvirtual machine (b) virtual machine Non-virtual Machine Virtual Machine

2.19 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Para-virtualization Presents guest with system similar but not identical to hardware Guest must be modified to run on paravirtualized hardwareF Guest can be an OS, or in the case of Solaris 10 applications running in containers

2.20 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition VMware Architecture

2.21 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Operating System Generation Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site SYSGEN program obtains information concerning the specific configuration of the hardware system Booting – starting a computer by loading the kernel Bootstrap program – code stored in ROM that is able to locate the kernel, load it into memory, and start its execution

2.22 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition System Boot Operating system must be made available to hardware so hardware can start it Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it Sometimes two-step process where boot block at fixed location loads bootstrap loader When power initialized on system, execution starts at a fixed memory location  Firmware used to hold initial boot code